Disk drive devices using various kinds of disks, such as optical disks, magneto-optical disks, flexible magnetic disks, and the like have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of indispensable storage devices for current computer systems. Moreover, the HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, in addition to the computers, due to their outstanding characteristics.
A magnetic disk used in an HDD has multiple concentric data tracks and servo tracks. Each servo track contains multiple servo data having address information. Each data track includes multiple data sectors containing user data recorded thereon. Data sectors are recorded between servo data discrete in the circumferential direction. A head element portion of a head slider supported by a swinging actuator accesses a desired data sector in accordance with address information in the servo data to write data to and retrieve data from a data sector.
An HDD positions a head slider using a swing actuator. Accordingly, if an HDD receives external vibration, the actuator vibrates so that the HDD has difficulty in performing accurate head positioning. To this end, an approach has been proposed that mounts a vibration sensor on the HDD and incorporates the vibration detected by the vibration sensor into the servo control for the head positioning (servo positioning) by means of feed-forward control to suppress the influence of the external vibration to the servo positioning. In particular, in a system having a plurality of HDDs arranged closely to each other such as a server system, vibrations caused by operation of other HDDs greatly affect the servo positioning so that a technique for detecting vibration by a vibration sensor and servo controlling responsive to the detected vibration is requisite.
The vibration sensor used in servo positioning detects vibration(s) in all directions parallel to the recording surface. This is because the actuator swings in the in-plane direction and vibration in the in-plane direction significantly affects the servo control. Typically, a rotational vibration sensor (RV sensor) is mounted on the HDD. The RV sensor directly detects rotational vibration or consists of two sensors for detecting vibration in a linear direction. The two sensors detect vibration (acceleration) in the X direction and the Y direction respectively, and the sensor can detect vibration(s) in all directions in the plane from those detected values.
For the RV sensor consisting of two sensors, the characteristics of the two sensors do not completely agree with each other due to manufacturing variations. If the difference between the characteristics of the two sensors is large, the possibility of erroneous detection by the RV sensor becomes higher. The RV sensor generally is mounted on a control circuit board fixed outside the HDD. This control circuit board slightly vibrates in the in-plane direction due to a warp of the substrate even when external vibration is applied in the Z direction. Therefore, the RV sensor sometimes erroneously detects vibration in the in-plane direction in vibration in the Z direction. This becomes clearly apparent if the control circuit board is thin, and therefore, will become a problem, particularly in a compact HDD.
The erroneous detection by the RV sensor leads to degradation in servo positioning and degrades the throughput (performance) of the HDD. Therefore, in order to prevent the degradation in servo positioning induced by the erroneous detection by the RV sensor, a technique which controls correction in the servo positioning using the vibration detected by the RV sensor is disclosed in a Japanese Patent Publication No. 2003-346439 (“Patent Document 1”). An HDD disclosed in Patent Document 1 calculates correction signals to be injected into a servo loop from outputs of the RV sensor, and further predicts the effect of the correction signals injected into the servo loop. The HDD then determines whether or not to inject the correction signals to the servo loop and dynamically controls gain of the RV sensor in accordance with the prediction.
As described above, the correction function for servo positioning using the RV sensor enabled and disabled depending on conditions can prevent degradation in servo positioning induced by erroneous detection by the RV sensor. However, the technique in the Patent Document 1 predicts the effect of the correction signals to determine the necessity of the correcting operation and the HDD does not actually observe the effect by the correction so that the predicted effect may not be accurately reflected to the actual servo positioning with vibration correction. On the other hand, determination whether or not to perform the vibration correction for the head positioning should not take much process time. Consequently, more accurate and efficient approach is required to determine whether or not to perform the vibration correction for the servo positioning.